The present invention relates to the cover of an aerosol spray container, either of the barrier or non-barrier type, and particularly relates to a cover of an aerosol container that is thin walled.
Aerosol spray containers have been used worldwide for decades. Typically, these containers are made of metal, such as steel or aluminum, and dispense either fluent materials or viscous materials and are either of the non-barrier type or the barrier type. Many fluent materials, and particularly those of lower viscosities, are dispensed from pressurized aerosol containers of the non-barrier type, wherein there is no separation between the fluent material to be dispensed and the pressurizing propellant within the container. In contrast, a barrier type dispensing container has a movable barrier within the container, such as a flexible diaphragm or a piston, where the material to be dispensed is at the side of the barrier towards the outlet and the propellant is on the other side of the barrier and pushes against the barrier and thereby forces the fluent materials of higher viscosities through the container dispenser valve.
The aerosol container comprises a generally cylindrically shaped container body having an open end with a cover attached to the open end usually by seaming or crimping, although welding or gluing is sometimes used. A spray, foam or stream nozzle is supported in the cover and communicates with the contents in the container body for dispensing the contents through the nozzle when the nozzle is activated.
Characteristic to the cover of most aerosol containers is a countersunk recess that projects into the container body and extends circumferentially in the radial vicinity of where the cover joins the container body. Radially inward of the recess the cover has a rounded, generally convex dome. The countersunk recess is for receiving a seaming chuck used in the process of joining the cover to the container body. However, the recess is the weakest and therefore most easily deformed part of the cover when the aerosol container is pressurized. Therefore, aerosol container covers have to be relatively thick walled to protect against the cover being deformed under pressure. The weakness at the recess in the cover is particularly critical when the pressure in the aerosol container increases due to ambient temperature increases during storage, transportation or manufacture.
Covers may also have a small ridge inwardly from the recess for the purpose of holding a cover cap.
The typical procedure for joining the cover to the container body involves a double seaming process. The container body is formed with a flange along the outer edge of the open end, and the cover is formed with a curl along its outer edge and a recess in the vicinity of the curled edge.
In the first seaming operation, the curl of the cover is interlocked with the flange at the top of the container body. The container body is positioned on a base plate, which may be rotatable, and the seaming chuck is positioned within the countersunk recess of the cover. The cover and the container body are interlocked by a seaming roller having a specially contoured groove. The seaming roller engages the curl of the cover and the flange of the container body and interlocks them by compressing them against the opposing resistance of the seaming chuck. During this first seaming operation, the cover and container body are rotated past the seaming roller by rotation of either the base plate or the chuck, or by both. A good quality first operation seam is neither too loose nor too tight and the flange of the container body is well tucked down in the radius of the curl of the cover. After the first seaming operation, the first seaming roller is retracted and no longer contacts the cover or the container body.
For the second seaming operation, a second seaming roller is used having a second groove profile different from that of the first seaming roller. The second groove profile is flatter than the profile of the first seaming roller and the groove profile is designed to press the curl of the cover and the flange of the container body tightly together to develop double seam tightness. Also during this step, sealing compound, if previously applied to the cover or otherwise used, is distributed evenly around the seam. After the double seaming operation is completed, the recess remains as part of the profile of the cover and does not change in form or shape even after the aerosol container is filled with a fluent material and pressurized.
The internal container pressure to which the cover is subjected and especially at its weakest region at the countersunk recess, has required that the cover wall be made relatively thick so that it does not permanently distort, evert or rupture from the high pressure encountered during filling, storage, transportation, use and testing. It is not unusual that during storage and transportation, the aerosol container is exposed to elevated ambient temperatures which elevate the internal pressure of the container, and this further stresses the recess in the cover.
Because of the potential dangers of rupture or distortion of an aerosol container, several government agencies have required that certain types of aerosol containers have particular strengths or distortion and burst resistances.
For example, a United States Department of Transportation regulation requires that an aerosol container having less than 27.7 fluid ounces or 819.2 ml capacity be able to withstand and not permanently distort at an internal pressure equal to the equilibrium pressure of its intended contents, including fluent material and propellant at 130.degree. F. or 54.4.degree. C. (122.degree. F. or 50.degree. C. is also a standard being adopted), and that the pressure in the container must not exceed 140 psig or 965 kPa or 9.65 bar, at 130.degree. F. or 54.4.degree. C. If the internal pressure in the aerosol container exceeds 140 psig or 965 kPa or 9.65 bar, special specifications for the can are required. Moreover, the U.S. Department of Transportation also requires that there be no permanent distortion of the aerosol container at 130.degree. F. or 54.4.degree. C. and that the container not burst at a pressure that is one and one half times as great as the pressure at 130.degree. F. or 54.4.degree. C. Thus, for example, if the equilibrium pressure of the aerosol container at 130.degree. F. or 54.4.degree. C. is 140 psig or 965 kPa or 9.65 bar, then the container should not burst at 210 psig or 1448 kPa or 14.48 bar.
In order to meet government mandated regulations and to withstand expected elevated internal pressure, the cover of a conventional aerosol container made of steel has a wall thickness in the range of 0.012 to 0.013 inch or 0.305 to 0.330 mm, while the wall thickness of a cover made of aluminum, depending on the alloy, is in the range of 0.012 to 0.018 inch or 0.305 to 0.457 mm. These requirements in the wall thickness of the cover produce a cover that weighs 16 to 20 grams if it is made of steel and has a diameter of approximately 2.47 inches, or a weight of 14.7 grams if it is made of an aluminum alloy and has a diameter of 2.47 inches and a wall thickness of about 0.016 inch or 0.406 mm.
If it were not for the inherent weakness of the chuck recess region in the aerosol container cover, covers could be made from a thinner walled metal producing substantial advantages both economically and environmentally. However, conventional wisdom is not to fabricate the covers of thinner walled metal, but rather to use thicker walled metal. The economic and environmental drawbacks of relatively thick walled aerosol container covers are great considering that approximately 10 billion aerosol containers are used yearly world-wide. From an economic standpoint, it is readily understood that a reduction in the thickness of the aerosol container cover can have a significant impact in reducing the need for ores and minerals used in producing these covers, particularly as these ores and minerals are in diminishing supply. With the cost of steel now at about U.S. $600 to $700 U.S. per ton, an aerosol container cover having half the conventional wall thickness results in a savings of about one half the steel required, or a savings of over $18 million per year for all U.S. consumers. Comparable or even greater savings are also achievable using aluminum covers. The average weight of a conventional thick walled cover, having a diameter of about 21/2 inches, or about 1 cm, is about 0.7 oz. (20 grams). If the wall thickness of the cover were reduced by half, a savings of 10 grams per cover or 30 billion grams (30 thousand tons) of steel would be achieved in the U.S. alone, and a savings of about 100 thousand tons of steel would be achieved worldwide. Comparable savings could result for aluminum covers.
In addition, more energy is consumed in obtaining the metal ore, in producing the metal, and in manufacturing aerosol container covers having relatively thick walls. The cost of transporting the metal for these covers at every stage from initial ore production, to transporting the metal for making the covers, to transporting the filled cans must also be considered. If the covers were of a thinner walled metal and were therefore lighter in weight, substantial savings in transportation costs would result. At approximately 30 tons per truck load, this translates to a thousand trucks per year for each stage of shipment. With three or four stages of shipment, this produces a very large saving in the cost of truck shipments.
Needless to say, each of the above economic factors also has an environmental impact. Adverse effects could be significantly reduced if the cover of the aerosol container could be reduced in wall thickness and still meet the stringent safety requirements mandated by various governments. In addition, the relatively thick walled cover of conventional aerosol containers are stiff and thus not easily deformed or crushed for enabling disposal or recycling.
Since countersunk recesses in container covers are traps for dust and dirt, a further advantage to be gained by eliminating these recesses is to provide a more sanitary container or one with easier access to exposed surfaces of the cover for cleaning them. Moreover, one method by which the industry combats the unsanitariness problem is to use a large shoulder overcap to prevent dust and dirt from accumulating within the countersunk recess. However, such overcaps add unnecessary cost to an aerosol container and pose additional environmental pollution problems. Thus, if the source of the problem, the recess, is eliminated, large shoulder overcaps are not necessary.